Molding device for the production of containers in thermoplastic material

ABSTRACT

A moulding device for the production of containers in thermoplastic material, by blowing or blow-drawing, including a mould with two mould halves mutually mobile and provided with a locking device with two lock elements extending over the total height of the respective mould halves and provided with a number of projecting fingers in catches spaced at intervals, one lock element being fixed on one mould half and the other lock element sliding on the other mould half under the action of an actuator device.

FIELD OF THE INVENTION

The present invention relates in general to the field of molding devicesfor blow-molding or stretch-blow-molding containers from heatedthermoplastic preforms.

More specifically, the invention relates to improvements made to thoseof these devices that comprise at least one mold comprising at least twohalf-molds that can be moved with respect to each other between an openposition in which they are parted from one another and a closed positionin which they are firmly pressed against one another via collaboratingrespective bearing faces defining a parting line, locking means beingprovided to lock the two half-molds in the closed position, whichlocking means comprising on at least one side of the mold, a first lockelement in the form of a hook secured fixedly to the first half-moldalong the edge of the bearing face thereof, a second lock element in theform of a hook inverted with respect to the previous one and mountedsuch that it can move on the second half-mold, and actuating meansfunctionally associated with said second lock element in such a way asto move the latter transversely between a locked position in which it isengaged with the first lock element to lock the two half-molds in theclosed position and an unlocked position in which it is disengaged fromthe first lock element to release the two half-molds that can then beparted from one another.

DESCRIPTION OF THE PRIOR ART

Document FR-A-2 646 802 discloses means for locking two half-molds inthe closed position which means comprise a plurality of coupling fingerssupported one above the other, coaxially, by a first half-mold and ableto be moved parallel to the axis of the mold to engage in a plurality ofrespective accommodating slots supported by the second half-mold.

Such locking means are satisfactory and are currently in commonplace usein molding devices of the “hinged” mold type.

However, these locking means do have several significant disadvantages.

One disadvantage lies in the fact that the fingers and accommodatingslots are supported in cantilever fashion by the first and secondhalf-molds respectively. As the blowing pressure (for example typicallyof the order of 40×10⁵ Pa) is applied, the supports of these fingers andaccommodating slots, which project radially, are subjected to a forcesubstantially tangential to the periphery of the mold. To prevent themfrom deforming or pulling out, these supports need to be solidly formed,and this increases the weight of the half-molds and also their cost.

Another disadvantage lies in the cantilevered structure of each finger,the base of which is set into a radially projecting support secured toone half-mold whereas, in the locked position, the free end of thefinger is held in a corresponding accommodating slot of a radiallyprojecting support secured to the other half-mold. Under the blowingforce, each finger is subjected to a bending/shear stress which, onceagain, entails that each finger be solidly formed, making it heavy andexpensive.

All these requirements lead to locking means that project appreciablyfrom the periphery of the mold whereas, in installations comprising agreat many molds and operating at high speed (rotary molding devices ofthe carousel type), the space available is very restricted. Furthermore,these locking means are heavy and increase the inertia of thehalf-molds, something which is detrimental to installations operating athigh speed.

Finally, it must be emphasized that the method of locking/unlockingthrough the axial movement of a plurality of superposed (“in line”)fingers entails relatively long travels so that the portion of eachfinger engaged in its corresponding slot is long enough and affordsappropriate mechanical strength: it is therefore possible to provideonly a restricted number of fingers and slots, spaced axially apart byan appreciable distance. This then finally results in a non-uniformdistribution of the forces over the height of the mold.

There is therefore a remaining need for molds with a simplified, lessbulky, less heavy, simpler and less expensive structure, this need beingfelt all the more keenly as higher production rates are being sought,entailing mechanisms that work more quickly with lower inertia.

SUMMARY OF THE INVENTION

For these reasons, the invention proposes a molding device as mentionedin the preamble which, being arranged in accordance with the invention,is characterized by the following combination of arrangements:

-   -   the locking means comprise two lock elements mounted        respectively on the two half-molds along the edges of the        respective bearing faces and extending substantially over the        entire height of said half-molds,    -   each lock element comprises a multiplicity of hook-shaped        projecting fingers distributed over the entire height of the        lock element and which, on one lock element face away front the        bearing face of the corresponding half-mold and, on the other        lock element face toward the bearing face of the corresponding        half-mold, said fingers of each lock element being substantially        parallel and separated from one another by spacings the        individual heights of which are slightly greater than the        individual heights of the fingers,    -   one of the lock elements being mounted fixedly on the        corresponding half-mold and the other lock element being        mounted, on the other half-mold, such that it can move so that        it can be slid parallel to the axis of the mold,    -   and actuating means functionally associated with said moving        lock element in order to move the latter between two positions,        namely:        -   a first position or unlocked position in which the fingers            of the moving lock element are positioned respectively level            with the spacings between the fingers of the fixed lock            element, in which position the two half-molds are not locked            together, and        -   a second position or locked position in which, with the two            half-molds pressed firmly together in the closed position,            the moving lock element is moved parallel to the axis of the            mold so that its fingers engage respectively with the            fingers of the fixed lock element, in which position the two            half-molds are locked together in their closed position.

In order to obtain a uniform distribution of the catching force over theentire height of the mold, it is desirable for the number of fingers tobe as high as possible in relation to the mechanical strength of saidfingers, whereby the height of the spacings between the fingers andtherefore the travel of the moving lock element between its locked andunlocked positions are as low as possible, which allows for more rapidclosure than can be obtained with the conventional mechanisms when theblowing device is a rotary one.

In one practical embodiment, the moving lock element is supported, onthe corresponding half-mold, by a guide member substantially parallel tothe axis of the mold, on which member said lock element is slidablymounted. It is then advantageous for the guide member to be a rodsecured to the half-mold, on which rod the moving lock element isslidably mounted, but prevented from rotating.

For preference, the actuating means for actuating the moving lockelement comprise:

-   -   a return spring able to return said lock element to its        aforesaid first position, and    -   a positive actuating member secured to said moving lock element        and able to act positively thereon in order to move it, against        the return force of the spring, toward its second position.

One simple solution then consists in contriving for the positiveactuating member to be able to be controlled, when the two half-moldsare in the closed position, by the other half-mold.

In practical terms, many embodiment variants may be anticipated: thefixed lock element may form an integral part of the correspondinghalf-mold or alternatively may be produced in the form of a part securedfixedly to the corresponding half-mold; likewise, the guide member thatguides the moving lock element may be supported directly by thecorresponding half-mold, or alternatively may be fixed to anintermediate plate, itself fixed to the half-mold.

In an embodiment which is very commonplace in practice, the arrangementsaccording to the invention find an application in molds of the hingedtype with the two half-molds articulated to one another in terms ofrotation on a shaft substantially parallel to one side of the partingline, said locking means then being provided on the opposite side ofsaid shaft about which the two half-molds rotate relative to oneanother.

It is also commonplace for each half-mold to comprise a shell holder towhich there is internally fixed a shell equipped with a moldinghalf-cavity the parting line being defined by the two shells pressedtogether when the mold is in the closed position, in which case,according to the invention, the locking means are supported by the twoshell-holders.

By virtue of the provisions according to the invention, a blow-moldingor stretch-blow-molding mold is produced in which locking is obtained bya single moving part with a relatively short travel; this travel islinear and parallel to the axis of the mold; finally, the moving part,which is greatly notched in many places to define the locking fingers,has a low mass and therefore a low inertia.

The result of this is that no angular movement of the locking parts issuperposed on the rotational movement of the half-molds during closureor opening and these half-molds are subjected to no parasiticacceleration as they rotate. The vertical movement component of themoving lock element has no appreciable influence over the behavior ofthe corresponding half-mold. This then finally yields more uniformmovements of the half-molds and, above all, shorter locking/unlockingtimes that provide an effective contribution to increasing the operatingrate of the molding device; indeed, for the same rotational speed, ifthe times needed for locking/unlocking are shorter, the time availablefor blowing can be increased.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood from reading the detaileddescription which follows of certain preferred embodiments given solelyby way of nonlimiting examples. In this description, reference is madeto the attached drawings in which:

-   -   FIGS. 1 to 4 are simplified perspective views of a mold of the        hinged type arranged according to the invention, shown in four        functionally different positions respectively;    -   FIG. 5 is a simplified view from above of the mold shown in FIG.        4, in the closed and locked position; and    -   FIG. 6 is a simplified view from above showing an embodiment        variant of the locking means according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

The arrangements according to the invention are improvements made tomolding devices for the blow-molding or stretch-blow-molding ofcontainers, such as bottles, from heated thermoplastic (for example PET)preforms. Such a molding device comprises at least one mold comprisingat least two half-molds (and possibly a third part that forms an axiallymovable mold bottom) which can be moved relative to one another betweenan open position in which they are parted from one another and a closedposition in which they are pressed firmly against one another bycollaborating respective faces defining a parting line, locking meansbeing provided to lock the two half-molds in the closed position andprevent them from parting or gaping when the blowing fluid is introducedunder very high pressure (for example typically of the order of 40×10⁵Pa).

Commonly, such molding devices may comprise a multiplicity of molds andmay therefore be arranged in the form of a rotary device or carouselwith the molds arranged at the periphery, the various functions ofopening/closing, locking/unlocking, etc. the molds possibly beingcontrolled in sequence as the carousel rotates by cam follower rollersborne by the molds and collaborating with guide cams mounted fixedly onthe outside of the rotary part.

Although the arrangements according to the invention can be applied toany type of mold, they are particularly applicable to molds equippedwith two half-molds that rotate one with respect to the other, or tohinged molds, which are currently in very widespread use, and it istherefore in the context of a hinged mold that the arrangements of theinvention will be set out in detail, without the protection beingrestricted to this one type of mold.

FIG. 1 illustrates, in simplified form, in perspective, the generalarrangement of a hinged mold, denoted in its entirety by the reference1, comprising two half-molds 1 a and 1 b (it also being possible for anaxially movable bottom—not shown—to be provided at the base of themold). The two half-molds respectively have two collaborating faces orbearing faces 2 a, 2 b which, in the closed position, define a partingline 3 (FIGS. 3, 4). The collaborating faces are hollowed out with,respectively, two half-cavities 4 a, 4 b which, when put together,define the molding volume 4 that has the external shape of the containerthat is to be obtained, or at least a major part of this shape, with theexclusion of its bottom.

In the example more particularly illustrated in FIG. 1, each half-mold 1a, 1 b has a composite structure and comprises an external framework orshell-holder 5 a, 5 b and an interior molding part or shell 6 a, 6 bwhich is fixed removably into the respective shell holder and comprisesthe aforesaid respective half-cavity 4 a, 4 b.

As can best be seen in FIGS. 3, 4 and 5, the half-molds 1 a, 1 b (inthis instance the shell-holders 5 a, 5 b) comprise, on one side,respective protruding cheeks 7 a, 7 b which are interleaved with oneanother in a superposed fashion and have passing through them a shaft 8arranged in the continuation of the parting line.

Furthermore, two projecting lugs 9 a, 9 b respectively support inrotation, via-spindles 10 a, 10 b distant from one another on each sideof the shaft 8, the ends of two actuating link rods 11 a, 11 b the othertwo respective ends of which are connected with the ability to rotatefreely on a spindle 12 which can be moved in a linear fashion (arrow 13)toward the spindle 8 or in the opposite direction, by drive means (notshown).

On the other side of the parting line 3 and on the opposite side to theshaft 8 there are locking means 14 intended to keep the two half-molds 1a, 1 b in the closed position as the blowing pressure is applied.

The locking means 14 comprise:

-   -   a first lock element 15 which is fixedly secured to the first        half-mold 1 a (the one on the left in FIG. 1) which extends        substantially along the edge of the bearing face 2 a thereof,        and    -   a second lock element 16 which is secured such that it can move        to the second half-mold 1 b (the one on the tight in FIG. 1) and        which extends substantially along the edge of the bearing face 2        b thereof,    -   the two lock elements 15, 16 extending substantially over the        entire height of said half-molds 1 a, 1 b.

Each lock element 15, 16 comprises a multiplicity of respectivehook-shaped projecting fingers 17, 18 distributed over the entire heightof the lock element. The fingers 17 of the first lock element 15 areparallel and face away from the bearing face 2 a of the correspondinghalf-mold 1 a and the fingers 18 of the second lock element 16 areparallel and face toward the bearing face 2 b of the correspondinghalf-mold 1 b. The fingers 17, 18 of each lock element 15, 16 have inpractice approximately the same height and are separated by spacings 19,20 respectively, the individual heights of which are slightly greaterthan the individual heights of the fingers.

The second lock element 16 is mounted on the half-mold 1 a such that itcan slide vertically, that is to say parallel to the axis of the mold.For this purpose, one simple embodiment is, as illustrated, for thehalf-mold 1 b to be equipped with a guide member substantially parallelto the axis of the mold and arranged along the edge of the bearing face2 b, it advantageously being possible for this guide member to consistof a rod 21 held in devises 22 projecting from the external face of thehalf-mold 1 b and on which rod the lock element 16 is mounted such thatit can slide but prevented from rotating.

Actuating means 23 are functionally associated with the lock element 16to move it between two positions, namely:

-   -   a first position or unlocked position (FIGS. 1, 2 and 3) in        which the fingers 18 of the moving lock element 16 are        positioned respectively level with the spacings 19 separating        the fingers 17 of the first lock element 15 and the spacings 20        between the fingers 18 are situated respectively level with the        fingers 17, in other words a position in which the two lock        elements are vertically offset from one another such that their        respective fingers 17, 18 do not interfere with each other, and    -   a second position or locked position (FIG. 4) in which the two        half-molds 1 a, 1 b are pressed firmly together (closed) and the        moving lock element 16 is moved vertically, parallel to the axis        of the mold, on the rod 21 so that its fingers 18 fit in behind        the fingers 17 of the fixed lock element and engage respectively        therewith, so that it becomes impossible to open the mold.

FIGS. 1 to 4 show four successive positions in the closing of the mold:

-   -   in FIG. 1, the mold 1 is open, the two half-molds 1 a, 1 b are        widely parted from one another, particularly with a view to        loading a preform;    -   in FIG. 2, the mold 1 is partially closed, the two half-molds 1        a, 1 b being brought closer together and the respective fingers        17, 18 being offered up to face the respective opposing spacings        19, 20;    -   in FIG. 3, the mold 1 is in the closed position, the two        half-molds 1 a, 1 b being pressed firmly together via their        respective bearing faces 2 a, 2 b defining the parting line 3,        the fingers 17, 18 being imbricated in one another;    -   and finally, in FIG. 4, the moving lock element 16 has been        moved (in this example raised) along the rod 21 so that the        fingers 17, 18 are hooked together, the mold 1 then being closed        and locked.

In order for the locking force to be distributed approximately uniformlyover the entire height of the mold, it is necessary for fingers 17, 18to be uniformly distributed over this entire height, defining betweenthem spacings that are as short as possible. It is therefore desirablefor the number of fingers to be determined as a compromise, that is tosay to be as high as possible in conjunction with their havingsufficient individual mechanical strength to allow them, withoutbreaking or deforming, to withstand the force individually applied tothem. One advantageous result of this arrangement is that the travel ofthe moving lock element 16 is short, leading to brief locking/unlockingtimes. To give a concrete example, the mold illustrated by way ofexample in FIGS. 1 to 4, designed for molding 1.5-liter bottles andhaving a height of approximately 35 cm, is equipped with about ten pairsof fingers 17, 18.

The actuating means 23 for actuating the moving lock element 16 may, ina simple way, comprise:

-   -   a return spring 24, interposed between the half-mold 1 b and the        lock element 16, to return the latter to its aforesaid first        position or unlocked position, and    -   a positive actuating member secured to the lock element 16 and        able to act positively thereon in order to move it, against the        return force of the spring 24, toward its second position.

By virtue of this arrangement it can be guaranteed that even unwantedmold closure will always occur with the fingers 17, 18 offset from oneanother.

When the mold forms part of a rotary molding device of the carouseltype, the positive actuating member may call upon a simple technicalsolution functionally associated with mold closure. For this purpose, asshown in FIGS. 1 to 4, one of the half-molds, for example the one 1 b onthe right, is made to support a movement transmission device 25comprising a moving rod 26 projecting beyond the bearing face 2 b andable to be contacted and pushed back by the other half-mold 1 a as themold is closed. The device 25 incorporates an appropriate mechanicalmeans (for example inclined surfaces controlled by the rod 26) orpreferably pneumatic means (the rod 26 controls a pneumatic piston)acting on a thrust rod (inside the spring 24 and not visible) able toraise the lock element 16.

The way in which the locking means 14 are embodied may give rise to manyvariants. In particular, in the example illustrated in FIGS. 1 to 5, thetwo lock elements 15, 16 form an integral part of the two respectivehalf-molds 1 a, 1 b, that is to say that the projecting fingers 17 ofthe first lock element 15 form an integral part of the first half-mold 1a (for example are cast with this half-mold or with the shell-holder 5 ain the example illustrated), while the devises 22 supporting the guiderod 21 of the second lock element 16 form an integral part of the secondhalf-mold 1 b (or of the shell-holder 5 b in the example illustrated).

However, it is possible to envisage forming the locking means in theform of separate elements attached to the half-molds, as illustrated inFIG. 6 (in which the mold has a different, quadrilateral, shape, onlythe shell-holders 5 a, 5 b being drawn, and the shells being omitted).As visible in this FIG. 6, the first lock element 15 is produced in theform of a plate 27 which is provided with the fingers 17 along one ofits edges; the plate 27 is fixed, for example by bolting at 28, to thecorresponding shell-holder 5 a. In the same way, the shaft 21 that actsas a guide for the second lock element 16 may be supported by a plate 29attached, for example by bolting at 30, to the second shell-holder 5 b.Such an arrangement of the first and/or second lock elements 15, 16 inthe form of attached parts may allow the manufacture of the half-moldsor shell-holders to be simplified and/or may allow the half-molds orshell-holders and the parts incorporating the hook-shaped fingers 17, 18to be made of different metals (for example aluminum casting and steel,respectively).

1. A molding device for blow-molding or stretch-blow-molding containersfrom heated thermoplastic preforms, said device comprising at least onemold comprising at least two half-molds that can be moved with respectto each other between an open position in which they are parted from oneanother and a closed position in which they are firmly pressed againstone another via collaborating respective bearing faces defining aparting line, locking means being provided to lock the two half-molds inthe closed position, wherein: the locking means comprise two lockelements mounted respectively on the two half-molds along the edges ofthe respective bearing faces and extending substantially over the entireheight of said half-molds, each lock element comprises a multiplicity ofhook-shaped projecting fingers distributed over the entire height of thelock element and which, on one lock element face away from the bearingface of the corresponding half-mold and, on the other lock element facetoward the bearing face of the corresponding half-mold, said fingers ofeach lock element being substantially parallel and separated from oneanother by spacings the individual heights of which are slightly greaterthan the individual heights of the fingers, one of the lock elementsbeing mounted fixedly on the corresponding half-mold and the other lockelement being mounted, on the other half-mold, such that it can move sothat it can be slid parallel to the axis of the mold, and actuatingmeans functionally associated with said moving lock element in order tomove the latter between two positions, namely: a first position orunlocked position in which the fingers of the moving lock element arepositioned respectively level with the spacings between the fingers ofthe fixed lock element, in which position the two half-molds are notlocked together, and a second position or locked position in which, withthe two half-molds pressed firmly together in the closed position, themoving lock element is moved parallel to the axis of the mold so thatits fingers engage respectively with the fingers of the fixed lockelement, in which position the two half-molds are locked together intheir closed position.
 2. The molding device as claimed in claim 1,wherein the number of fingers is as high as possible in relation to themechanical strength of said fingers, whereby the height of the spacingsbetween the fingers and therefore the travel of the moving lock elementbetween its locked and unlocked positions are as low as possible.
 3. Themolding device as claimed in claim 1, wherein the moving lock element issupported, on the corresponding half-mold, by a guide membersubstantially parallel to the axis of the mold, on which member saidlock element is slidably mounted.
 4. The molding device as claimed inclaim 3, wherein the guide member is a rod secured to the half-mold, onwhich rod the moving lock element is slidably mounted, but preventedfrom rotating.
 5. The molding device as claimed in claim 1, wherein theactuating means for actuating the moving lock element comprise: a returnspring able to return said lock element to its aforesaid first position,and a positive actuating member secured to said moving lock element andable to act positively thereon in order to move it, against the returnforce of the spring, toward its second position.
 6. The molding deviceas claimed in claim 5, wherein the positive actuating member is able tobe controlled, when the two half-molds are in the closed position, bythe other half-mold.
 7. The molding device as claimed in claim 1,wherein the fixed lock element forms an integral part of the half-mold.8. The molding device as claimed in claim 1, wherein the fixed lockelement is produced in the form of a part secured fixedly to thecorresponding half-mold.
 9. The molding device as claimed in claim 3,wherein the guide member that guides the moving lock element issupported directly by the corresponding half-mold.
 10. The moldingdevice as claimed in claim 3, wherein the guide member that guides themoving lock element is fixed to an intermediate plate, itself fixed tothe half-mold.
 11. The molding device as claimed in claim 1, wherein themold is of the hinged type with the two half-molds articulated to oneanother in terms of rotation on a shaft substantially parallel to oneside of the parting line and wherein said locking means (14) areprovided on the opposite side of said shaft about which the twohalf-molds rotate relative to one another.
 12. The molding device asclaimed in claim 1, in which each half-mold comprises a shell holder towhich there is internally fixed a shell equipped with a moldinghalf-cavity the parting line being defined by the two shells pressedtogether when the mold is in the closed position, wherein the lockingmeans are supported by the two shell-holders.